Solid state image sensor

Abstract

A solid state image sensor includes a semiconductor substrate of a first conductivity type, in a plurality of cell units formed in the surface region of the semiconductor substrate. Each of the cell units includes a photo detector portion and an electric charge reading portion. The photo detector portion includes a first impurity region of a second conductivity type formed in the surface region of the semiconductor substrate and a second impurity diffusion region of the first conductivity type formed in the surface region of the first impurity region. The electric charge reading portion includes a third impurity region of the second conductivity type formed in the surface of the semiconductor substrate, a first insulation film formed on the third impurity diffusion region and an electrode formed in the first insulation film.

We claim: 
     
       1. A solid state image sensor comprising: a semiconductor substrate of a first conductivity type,   plurality unit cells formed in a surface region of said semiconductor substrate,   each one of said unit cells comprising a photodetector portion for detecting incident light energy and an electric charge reading portion for reading electric charges generated by said photo detector portion,   said photo detector portion comprising said semiconductor substrate, a first impurity region of a second conductivity type formed in the surface region of said semiconductor substrate and a second impurity region of said first conductivity type formed in a substantial portion of a surface region of said first impurity region,   said electric charge reading portion comprising a third impurity region of said second conductivity type formed in the surface region of said semiconductor substrate, a first insulation film formed on said third impurity region and an electrode formed on said first insulation film,   wherein said second impurity region of said photo detector portion and said electrode of said electric charge reading portion have edge portions which overlap one another by a first distance, and wherein said first impurity region of said photo detector and said electrode of said electric charge reading portion have edge portions which overlap one another by a second distance.   
     
     
       2. A solid state image sensor according to claim 1, wherein said second distance is greater than a junction depth of said second impurity region. 
     
     
       3. A solid state image sensor according to claim 1, wherein an impurity concentration of said second impurity region is at least 1×10 18  /cm 3 .